July Atlantic hurricane outlook

It's mid-July, and we have yet to see a named storm form in the Atlantic this month. The computer models are not predicting any development through at least July 20, and if we make it all the way to the end of the month without a named storm forming, it will be the first July since 2009 without a named storm. Since the current active hurricane period began in 1995, 13 of 17 years (76%) have had a named storm form during July. The busiest July occurred in 2005, when five named storms and two major hurricanes formed. These included Hurricane Dennis and Hurricane Emily--the strongest hurricanes ever observed so early in the season. Only eight major hurricanes have formed in July since record keeping began in 1851. As seen in Figure 1, most of the last half of July activity occurs in the Gulf of Mexico and waters off the Southeast U.S. coast. These type of storms form when a cold front moves off the U.S. coast and stalls out, with the old frontal boundary serving as a focal point for development of a tropical disturbance (as happened for Alberto, Beryl, Chris, and Debby in 2012.) There will be at least two cold fronts moving off the U.S. Mid-Atlantic coast over the next two weeks. The first of these fronts will push offshore around July 20, and we will need to watch the waters offshore of North Carolina for development then. Formation potential will be aided by ocean temperatures that are about 0.7°C (1°F) above average along the U.S. East Coast.

Figure 1. Tracks of all tropical storms and hurricanes 1851 - 2006 that formed July 16-31. The U.S. coast from North to Texas are the preferred strike locations. Only a few storms have formed in the tropical Atlantic and Caribbean in July. Wind shear is typically too high and SSTs too cool in July to allow African waves in the Caribbean and tropical Atlantic to develop into tropical storms. However, a few long-track "Cape Verdes" hurricanes have occurred in July, spawned by tropical waves that came off the coast of Africa. African tropical waves serve as the instigators of about 85% of all major hurricanes.

Sea Surface Temperatures: slightly above averageThe departure of Sea Surface Temperatures (SST) from average over the tropical Atlantic between Africa and Central America was about 0.3°C above average during June (Figure 3.) This figure has not changed much over the first two weeks of July. These temperatures are not warm enough to appreciably affect the odds of a July named storm or hurricane. The strength of the Azores-Bermuda high has been near average over the past two weeks, driving near-average trade winds. The latest 2-week run of the GFS model predicts continued average-strength trade winds through late-July, so SSTs should remain about 0.3°C above average during this period, due to average amounts of cold water mixing up from below due to the wind action on the water.

Figure 3. Sea Surface Temperature (SST) departure from average for July 12, 2012. SSTs were 0.3°C above average over the tropical Atlantic's Main Development region for hurricanes, from Africa to Central America between 10° and 20° North Latitude. Note the large region of above average SSTs along the Equatorial Pacific off the coast of South America, the hallmark of a developing El Niño episode. Image credit: NOAA/NESDIS

El Niño on the way?For two consecutive weeks, ocean temperatures 0.5 - 0.6°C above average have been present in the tropical Eastern Pacific, which is right at the threshold for a weak El Niño episode. NOAA's Climate Prediction Center has issued an El Niño Watch, and gives a 61% chance that El Niño conditions will be present during the August - September - October peak of the Atlantic hurricane season. The likely development of a full-fledged El Niño episode means that Atlantic hurricane activity will probably be suppressed in 2012, due to the strong upper-level winds and high wind shear these events typically bring to the tropical Atlantic.

Figure 4. Sea Surface Temperature (SST) departure from average for the the equatorial Eastern Pacific (the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region"). El Niño conditions exist when the SST in this region rises 0.5°C above average. As of July 9, 2012, SSTs in the Niño 3.4 region had risen to 0.5°C above average. To be considered an "El Niño episode", El Niño conditions must occur for five consecutive months, using 3-month averages. Image credit: NOAA Climate Prediction Center.

Wind shear: above averageWind shear is usually defined as the difference in wind between 200 mb (roughly 40,000 foot altitude) and 850 mb (roughly 5,000 foot altitude). In most circumstances, wind shear above 20 knots will act to inhibit tropical storm formation. Wind shear below 12 knots is very conducive for tropical storm formation. High wind shear acts to tear a storm apart. The jet stream has two bands of strong high-altitude winds that are currently bringing high wind shear to the Atlantic. The southern branch (subtropical jet stream) is bringing high wind shear to the Caribbean, and the northern branch (polar jet stream) is bringing high wind shear to the waters offshore of New England. This configuration often leaves a "hole" of low shear between the two branches, off the Southeast U.S. coast and over the Gulf of Mexico. The jet stream is forecast to maintain this two-branch pattern over the coming two weeks. Wind shear has been about 10 - 20% higher than average over the first two weeks of July, and is predicted to be mostly above average for the coming two weeks. This will cut down on the odds of a July storm.

Figure 5. Vertical instability over the Caribbean Sea in 2012 (blue line) compared to average (black line.) The instability is plotted in °C, as a difference in temperature from near the surface to the upper atmosphere. Thunderstorms grow much more readily when vertical instability is high. Instability has been lower than average, due to an unusual amount of dry air in the atmosphere, reducing the potential for tropical storm formation. Image credit: NOAA/NESDIS/CIRA.

Dry air: above averageAs seen in Figure 5, there has been an unusual amount of dry, stable air in the Caribbean this year creating low levels of vertical instability. This has occurred due to a combination of dry air from Africa, and upper-atmosphere dynamics creating large areas of sinking air that dry as they warm and approach the surface. The Gulf of Mexico and tropical Atlantic between the coast of Africa and the Lesser Antilles have also seen low vertical instability this summer. June and July are the peak months for dry air and dust coming off the coast of Africa, and the Saharan dust storms have been quite active over the past two weeks. Expect dry air to be a major deterrent to any storms that try to form in the tropical Atlantic during July.

Steering currents: averageThe predicted steering current pattern for the next two weeks is a typical one for July. We have an active jet stream bringing many troughs of low pressure off the East Coast of the U.S. These troughs are frequent enough and strong enough to recurve any tropical storms or hurricanes that might penetrate north of the Caribbean Sea. Steering current patterns are predictable only about 3 - 5 days in the future, although we can make very general forecasts about the pattern as much as two weeks in advance. There is no telling what might happen during the peak months of August, September, and October--we might be in for a repeat of the favorable 2010 and 2011 steering current pattern, which recurved most storms out to sea--or the unfavorable 2008 pattern, which steered Ike and Gustav into the Gulf of Mexico.

Summary: a below average chance of a July tropical stormGiven that none of the computer models are forecasting tropical storm formation in the coming seven days, SSTs are only slightly above average, and wind shear and vertical stability are above average, I'll go with a 30% chance of a named storm forming in the Atlantic during the remainder of July.

Figure 6. Hurricane Emilia over the Eastern Pacific at 20:35 UTC July 10, 2012. At the time, Emilia was a Category 3 hurricane with 125 mph winds. Emilia peaked earlier in the day as a Category 4 storm with 140 mph winds--the strongest hurricane in the East Pacific so far in 2012. Image credit: NASA.

An active Eastern Pacific hurricane seasonIt's been a very active start to the Eastern Pacific hurricane season, where we've already had six named storms, four hurricanes, and three intense hurricanes. A typical season has 4 named storms, 2 hurricanes, and 0 intense hurricanes by July 14. The formation of Tropical Storm Fabio on July 12 marks the 4th earliest formation of the Eastern Pacific's season's sixth storm. The record is held by the year 1985, when the season's sixth storm formed on July 2. Record keeping began in 1949.

Have a great weekend, everyone, and I'll be back Monday with a new post.

.............this is from this morning i think..there IS some lil thing crossing from africa we need to keep an eye on the next few days, august is drawing closer and the gulf temps are cooking in the high 80's when and if it gets here

Quoting wxchaser97: Thanks, I know that half the people here ar from Fl it seems and most others from the south so I just want to add some diversity. Also I know I'm around 50 miles from Ann Arbor so my weather and Dr M. weather is usually the same.That would not be good because there would be nothing in the tropics to talk about.

..keep posting ok, its a good thing people from all over post their weather, last evening we had some folks from out west posting

Quoting wxchaser97:Thanks, I know that half the people here ar from Fl it seems and most others from the south so I just want to add some diversity. Also I know I'm around 50 miles from Ann Arbor so my weather and Dr M. weather is usually the same.That would not be good because there would be nothing in the tropics to talk about.

Quoting etxwx:Hey wxchaser97, just wanted to say thanks for the weather updates from Michigan and the upper mid-west. I have family up there and appreciate the info.

Thanks, I know that half the people here ar from Fl it seems and most others from the south so I just want to add some diversity. Also I know I'm around 50 miles from Ann Arbor so my weather and Dr M. weather is usually the same.

Quoting windshear1993:also that eruption calmed the tropics for a few years

That would not be good because there would be nothing in the tropics to talk about.

Quoting wxchaser97:Everyone is wishing a summer like this was happening:Also on July 14, 1992, Detroit had a high temperature of 83 degrees. This is about the average high temperature for mid July, but it was the warmest day in Detroit in July of 1992, the second coldest July on record and part of the "Cold Summer of 1992".

CONVECTION HAS BLOSSOMED RECENTLY AS EMILIA MOVED OVER A TONGUE OFRELATIVELY WARM WATERS. EMILIA HAS NOT WEAKENED SINCE THE PREVIOUSADVISORY...AND SATELLITE ESTIMATES STILL SUPPORT AN INITIALINTENSITY OF 45 KNOTS. NO SIGNIFICANT CHANGE IN INTENSITY ISEXPECTED TODAY WHILE EMILIA IS STILL INFLUENCED BY THE WARMERWATERS. THE CYCLONE WILL MOVE BACK OVER COOL WATERS ON SUNDAY...AND THE EXPECTED WEAKENING SHOULD RESUME. EMILIA IS EXPECTED TOBECOME A POST-TROPICAL REMNANT LOW BY SUNDAY NIGHT OR MONDAY.

EMILIA IS A SHALLOW CYCLONE WELL EMBEDDED WITHIN THE TROPICAL TRADEWINDS. THEREFORE...A GENERAL TRACK TO THE WEST AT ABOUT 12 TO 14KNOTS IS ANTICIPATED THROUGH THE FORECAST PERIOD.

FABIO IS DISPLAYING A RAGGED EYE IN INFRARED IMAGERY...AND RECENTAMSU DATA INDICATE THAT THE HURRICANE CONTINUES TO HAVE A CLOSEDEYEWALL. THE MAXIMUM WINDS ARE STILL ESTIMATED TO BE 80 KT BASEDON DVORAK NUMBERS AND ESTIMATES OF 76 AND 80 KT FROM THE AMSU DATA.THE IMPACTS OF NORTHEASTERLY SHEAR ON FABIO SHOULD LESSEN AFTERABOUT 24 HOURS...BUT BY THAT TIME...THE HURRICANE WILL BE LOCATEDOVER OVER SUB-26C WATER. SOME FLUCTUATIONS IN INTENSITY ARE STILLPOSSIBLE OVER THE NEXT DAY OR SO FOLLOWED BY A GRADUAL WEAKENINGOVER THE COOLER WATERS ON SUNDAY. THE CYCLONE COULD THENBECOME A REMNANT LOW BY DAY 4. THE NHC INTENSITY FORECAST IS CLOSETO A BLEND OF THE SHIPS...LGEM...AND FSU SUPERENSEMBLE.

THE INITIAL MOTION REMAINS 285/9 KT. LITTLE CHANGE IN THE HEADINGIS EXPECTED FOR THE NEXT 36 HOURS WHILE FABIO REMAINS TO THE SOUTHOF THE SUBTROPICAL RIDGE. AN AMPLIFYING TROUGH ALONG THE U.S. WESTCOAST SHOULD PRODUCE A BREAK IN THE RIDGE BY DAY 2...AT WHICH TIMEFABIO WILL BEGIN TO TURN NORTHWESTWARD AND THEN NORTHWARD. THEREIS SOME SEPARATION BETWEEN THE GFS/UKMET SOLUTIONS AND THE ECMWF.THE LATTER SHOWS A SHARPER AND SLOWER TURN TOWARD THE NORTH. BUTALL IN ALL...THE MODELS ARE GREATER-THAN-NORMAL AGREEMENT...AND THENHC FORECAST LIES NEAR THE MIDDLE OF THE GUIDANCE ENVELOPE.

Everyone is wishing a summer like this was happening:Also on July 14, 1992, Detroit had a high temperature of 83 degrees. This is about the average high temperature for mid July, but it was the warmest day in Detroit in July of 1992, the second coldest July on record and part of the "Cold Summer of 1992".

Quoting Tropicsweatherpr:I have been following this big complex inside Africa and after 4 days it still looks fairly good. Let's see when it emerges West Africa early next week,how it behaves in a new enviroment.

Twenty years ago, during another weak El Niño, CSU rightly predicted just one major hurricane. That turned out to be the Category 5 goliath, Andrew, which pummeled South Florida in late August as the first named storm in an otherwise sleepy storm season.

Quoting charlottefl:

Twenty years ago, during another weak El Niño, CSU rightly predicted just one major hurricane. That turned out to be the Category 5 goliath, Andrew, which pummeled South Florida in late August as the first named storm in an otherwise sleepy storm season.

Quoting mcluvincane:Has hurricane season ended already? We haven't had much to talk about. I mean not even an invest. What gives? Will it be like this in August?

Ended? Hurricane season hasn't even begun. Generally we've had nothing by this time, so to have bagged four already is pretty amazing.

I think the absolutely funniest thing that could happen is for there to be no more named storms this year. Imagine that: 2012 finishes at 4-1-0, with all of those before July. This forum would go nuts. So would the NHC. And the UK Met Office. And Dr. Grey...

But that won't happen; things will start picking up shortly, and even a relatively weak season will still yield at least another half-dozen or more storms, with some of those hurricanes. Just hang on...

Quoting windshear1993:when andrew formed there wasnt elnino in fact it was neutral at the time it formed..just a simple fact

Twenty years ago, during another weak El Niño, CSU rightly predicted just one major hurricane. That turned out to be the Category 5 goliath, Andrew, which pummeled South Florida in late August as the first named storm in an otherwise sleepy storm season.

THERE IS A CHANCE FOR THUNDERSTORMS TODAY AND TONIGHT. THE BESTCHANCE THROUGH THE AFTERNOON HOURS WILL BE ALONG AND WEST OF USHIGHWAY 23. BRIEF HEAVY DOWNPOURS WILL BE POSSIBLE WITH ANY STORMTHAT DEVELOPS. THESE STORMS WILL NOT BE SEVERE AS THEY TRACK TOTHE NORTHEAST AT 20 MPH.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THERE IS A CHANCE OF THUNDERSTORMS THROUGH AT LEAST MIDDAY SUNDAY ASAN UPPER LEVEL LOW PRESSURE SYSTEM TRAVERSES THE AREA.

THERE IS ANOTHER CHANCE OF THUNDERSTORMS TUESDAY NIGHT ANDWEDNESDAY AS A COLD FRONT SLOWLY ADVANCES DOWN FROM THE NORTH.

All eyes are on the solar wind data to note the expected passage on Saturday of a Coronal Mass Ejection (CME) from Thursday's solar event. SWPC expects G1 (minor) with the chance of attaining G2 (moderate) Geomagnetic Storm activity after 9:00 a.m. EDT (1300 UTC) on July 14. Elsewhere the S1 (minor) Solar Radiation Storm lingers, and Region 1520 has been quiet. Updates here as conditions warrant.

Effective Wednesday, July 25, 2012, at 1600 UTC (10:00 AM MDT), SWPC will modernize its geomagnetic storm watch products. These products will now be issued relative to the highest expected geomagnetic storm category (NOAA Scale) and will be based on the 3-hour geomagnetic K-index rather than the 24-hour A-index. Watch products will still be valid for the entire UTC day, just as they are under the A-based watches today. This change will better align SWPC's geomagnetic watch products with its geomagnetic warning and alert products and NOAA Scale designations. Product Subscription Service customers are not required to take any action regarding this change. The current A-based watches contain expected geomagnetic storm scale (G-level) information so all subscriptions will be automatically transferred to the new G-based watch products.

A slow moving low pressure system will traverse the state this weekend, proving a chance of some thunderstorms. Another round of hot weather can be expected Monday and Tuesday before a cold front drops down from the north, providing a chance of rain Wednesday and bringing cooler temperatures to the area by late next week.

(1) THE AREA OF CONVECTION PREVIOUSLY LOCATED NEAR 20.0N 146.5E, IS NOW LOCATED NEAR 18.9N 144.1E, APPROXIMATELY 325 NM NORTH OF ANDERSEN AFB, GUAM. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS A CURVED CONVECTIVE BAND EXTENDING SOUTHWESTWARD OF A SMALL CENTRAL DENSE OVERCAST (CDO) CONVECTIVE ELEMENT LOCATED OVER THE SUSPECTED LOW-LEVEL CIRCULATION CENTER (LLCC). A LARGER AREA, EAST AND NORTHEAST OF GUAM, OF STRONGER CONVERGENT FLOW IS ALSO FUELING DEEP CONVECTION; HOWEVER, THESE CLOUD TOPS ARE QUICKLY SHEARING OFF TO THE EAST-SOUTHEAST. A 140412Z TRMM 37 GHZ IMAGE DEPICTS SHALLOW AND BROAD CYCLONICALLY TURNING CLOUD LINES OVER THE WESTERN PORTION OF THE LLCC AND THE 85 GHZ IMAGE DETAILS THE STRONG CONVECTION CONTAINED WITHIN THE SMALL CDO FEATURE TO THE EAST OF THE LLCC. SCATTEROMETRY DATA FROM 140223Z SHOWS A 05-10 KNOT LLCC LOCATED NEAR 19.5N 143.5E WITH 25-30 KNOT SOUTH-SOUTHEASTERLY WINDS CONVERGING INTO THE PREVIOUSLY MENTIONED RAINBAND. UPPER-LEVEL ANALYSIS SHOWS A VERY COMPLEX PATTERN WITH TWO TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) CELLS LOCATED NEAR THE LLCC. THERE IS AN ELONGATED TUTT CELL LOCATED WEST OF THE LLCC NEAR 16N 134E WHICH IS PROVIDING FOR SOME CONVERGENT FLOW INTO THE OTHERWISE EXCELLENT DIVERGENT FLOW FROM A NEAR EQUATORIAL RIDGE ANTICYCLONIC CENTER LOCATED APPROXIMATELY ONE DEGREE WEST OF THE LLCC. ANOTHER SMALLER, MORE WELL-DEFINED, TUTT CELL EXISTS NORTH OF THE LLCC NEAR 25N 145E, AND IS PROVIDING FOR ENHANCED POLEWARD OUTFLOW. ADDITIONALLY, THE LARGER TUTT TO THE EAST, WHICH HAS MULTIPLE EMBEDDED TUTT CELLS, IS PROVIDING FOR ENHANCED EASTWARD EXHAUST. SEA SURFACE TEMPERATURES NEAR THE MARIANAS ISLANDS ARE EXTREMELY WARM (30-32 CELSIUS), OCEAN HEAT CONTENT REACHES A MAXIMUM NEAR GUAM, AND THE 26 DEGREE CELSIUS ISOTHERM IS DEEPEST IN A BELT SPANNING FROM APPROXIMATELY 10-20N TO 125-160E. NUMERICAL MODEL GUIDANCE PROJECTS THE LLCC TO SLOWLY TRACK WEST-SOUTHWEST AND DEVELOP STRONG SOUTHEASTERLY GRADIENT WINDS BETWEEN THE LLCC AND A BUILDING DEEP-LAYERED SUBTROPICAL RIDGE TO THE NORTHEAST. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 12 TO 17 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1008 MB. DUE TO THE EXTREMELY FAVORABLE UPPER-LEVEL ENVIRONMENT AND VERY WARM OCEAN PARAMETERS, THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS UPGRADED TO MEDIUM.